The present disclosure relates to a magnetoresistive element, and more specifically, to a magnetoresistive element formed of a memory element, for example.
The magnetic random access memory (MRAM) performs the data storage using a magnetization direction of a magnetic material, so that high speed and nearly unlimited (1015 times or more) rewriting can be made, and therefore the MRAM has already been used in fields such as industrial automation and an airplane. The MRAM is expected to be used for code storage or a working memory in the near future because of the high-speed operation and high reliability. However, the MRAM has challenges related to lowering power consumption and increasing capacity. This is a basic problem caused by the recording principle of the MRAM, i.e., the method of inverting the magnetization using a current magnetic field generated from a wiring. As a method of solving this problem, a recording method not using the current magnetic field, i.e., a magnetization inversion method, is under review. Among them, a spin injection-type magnetoresistive effect element that uses magnetization inversion by spin injection attracts attention.
The magnetization inversion by spin injection is a phenomenon in which a spin-polarized electron that has passed through a magnetic material is injected into a different magnetic material and thus, magnetization inversion is caused in the different magnetic material. The spin injection-type magnetoresistive effect element uses magnetization inversion by spin injection, and thus has such advantages that a writing current is not increased even if the size of the element is reduced, scaling is possible because a writing current value is reduced in proportion to the element volume, and the cell area can be reduced, as compared with the MRAM that performs magnetization inversion based on the external magnetic field. In addition, the spin injection-type magnetoresistive effect element does not need a word line for generating a recording current magnetic field, which is necessary in the MRAM, and thus has such an advantage that a device structure and a cell structure are simple.
Incidentally, in order to achieve a spin injection-type magnetoresistive effect element with high reliability, a reference layer (referred to also as a pinned layer) that pins the magnetization direction needs to have a sufficiently high spin torque resistance as compared with the recording layer. In addition, the reference layer needs to have a sufficiently high external magnetic field resistance to avoid unnecessary magnetization inversion of the reference layer caused due to an external magnetic field. In Japanese Patent Application Laid-open No. 2012-248688, in order to increase the spin torque resistance of the reference layer, the volume is increased by increasing the area of the reference layer with respect to the area of the recording layer.